Calibrating geologic strata, dinosaurs, and other fossils at Dinosaur Provincial Park (Alberta, Canada) using a new CA-ID-TIMS U–Pb geochronology

Abstract

The 100 m thick stratigraphic section exposed at Dinosaur Provincial Park (DPP, southern Alberta) contains bentonites that have been used for more than 30 years to date DPP's rocks and fossils using the K-Ar decay scheme. Limited reproducibility among different vintages of K-Ar and 40Ar/39Ar ages inhibited the development of a high resolution chronostratigraphy. Here we employ and further test a recently completed CA-ID-TIMS U–Pb geochronology and associated age-stratigraphy model to update temporal constraints on the Park’s bentonites, formational contacts, and other markers. In turn, we document rock accumulation rates, and calibrate ages and durations of informal megaherbivore dinosaur assemblage zones and other biozones. Weighted mean 206Pb/238U ages from five bentonites range from 76.718 ± 0.020 Ma to 74.289 ± 0.014 Ma (2σ internal uncertainties) through an interval of 88.75 m, indicating a duration of ~2.43 Myr and an overall rock accumulation rate of 3.65 ± 0.04 cm/ka. An increase in rate above the Oldman-Dinosaur Park formational contact conforms to a regionally expressed pattern of increased accommodation at ~76.3 Ma across Alberta and Montana. Palynological biozone data suggest a condensed section/hiatus in the uppermost portion of the Oldman Formation. Dinosaur assemblage zones exhibit durations of ~600–700 kyr and are significantly shorter than those in the overlying Horseshoe Canyon Formation. A decreased rate in dinosaur-assemblage turnovers in the last eight million years of the Mesozoic in western Canada may be explained by withdrawal of the Western Interior Seaway and the expansion of ecologically homogenous lowlands in its wake.

Stratigraphic architecture of the Belly River Group (Campanian, Cretaceous) in the plains of southern Alberta: Revisions and updates to an existing model and implications for correlating dinosaur-rich strata

“…For example, the reciprocal wedged-shaped geometries of the Oldman and Dinosaur Park formations across southern Alberta suggest that some fossil locations that occur in the lower one-half of the Dinosaur Park Fm at northern locations (e.g., Hilda, Sandy Point, Jenner, and Dinosaur Provincial Park) likely are time equivalent with fossil locations that occur in the upper one half of the Oldman Fm at south-eastern locations (e.g., Manyberries area). This possibility has been mentioned or discussed previously [ 26 – 28 ] based on taxonomic comparisons, and the hypothesis can now be tested more rigorously using high-resolution U-Pb CA-ID-TIMS dating of bentonites from each location [ 9 , 11 , 12 ].…”

“… Also included is a measured section of fossiliferous strata from the Red Deer River at Dinosaur Provincial Park. All sections are correlated to one another and well logs using local marker beds, formational contacts, and formation thicknesses [ 1 , 7 , 11 , 12 ]. The five U-Pb radiometric ages from the Oldman, Dinosaur Park and Bearpaw formations at Dinosaur Provincial Park are from Ramezani et al [ 11 ] and Eberth et al [ 12 ].…”

“…All sections are correlated to one another and well logs using local marker beds, formational contacts, and formation thicknesses [ 1 , 7 , 11 , 12 ]. The five U-Pb radiometric ages from the Oldman, Dinosaur Park and Bearpaw formations at Dinosaur Provincial Park are from Ramezani et al [ 11 ] and Eberth et al [ 12 ]. Also note the sandy lower one-half and muddy upper one-half of the Dinosaur Park Fm.…”

“…The Foremost Fm is a coaly, marine-to-paralic unit that prograded eastward and marked the retreat from Alberta of marine environments (Pakowki/Lea Park Fm) from ~80–78 Ma [ 8 ]. The Oldman Fm is a predominantly nonmarine alluvial unit that records the maximum retreat of the WIS from Alberta and western Saskatchewan at ~78–77 Ma [ 1 , 7 , 11 , 12 ]. It thickens considerably in southwestern Alberta where it replaces the Dinosaur Park Fm and becomes younger up-section.…”

“…As the Oldman Fm loses distinction to the north (~Twp 40), the Foremost and Dinosaur Park formations amalgamate, but are difficult to differentiate. The Dinosaur Park Fm is a marine-paralic and nonmarine alluvial unit that records the transgression of the Bearpaw Sea across western Saskatchewan and southern Alberta from ~77–74 Ma [ 1 , 7 , 9 , 11 , 12 , 14 ]. It pinches out stratigraphically to the southwest in the Lethbridge area and thins toward the southeast (Manyberries area) where it extends into northern Montana.…”